The present invention relates to the identification of a mold with a glass container or like molded article, and more particularly to the design of reliable inspection apparatus, suited to detecting "dot codes".
In the manufacture of glass containers and like articles in a press mold, casting mold, or blow mold, any malformations of the mold are transferred onto the article. It is necessary in such applications to identify the mold in which a specific defective article has been produced and sort out all articles made in this mold. This need has been particularly acute in the high speed production of glass containers, in which the molds are subjected to destructive thermal and mechanical influences. The generally accepted approach to this problem has been to furnish each mold with a marking, to be transferred onto all articles molded thereby.
A variety of mold identification code markings have been adopted, among the most popular of which is the dot-code; the present invention is especially applicable to the accurate detection of this type of code. Typical of the prior approaches to mold number reading is the system of commonly assigned U.S. Pat. No. 4,201,338. In the '338 system and similar prior art mold number readers, a light source illuminates an area of the bottle's heel large enough to account for variations of bottle shape, relative placement of the photodetector, and other geometric factors. Light which has been reflected from a dot-code marking on the bottle is focused into the photodetector using a imaging-type optical system, and processed to extract the mold identification information. Such systems do not clearly discriminate between background light and the light produced by the code marking, and require elaborate filtering to minimize this problem. More significantly, such systems have a quite limited depth of field, and hence are very sensitive to variations in bottle motion and other disturbances.
Accordingly, it is a principal object of the invention to provide improved method and apparatus for identifying code markings on glass containers and other articles. As a related object, such apparatus should enjoy reliable performance under high speed operating conditions.
Another object is to provide a durable system which is easily adapted to a variety of operating environments.
A further object is to achieve a high degree of accuracy in the face of possible sources of "noise" in the output signals of such apparatus. These devices should enjoy increased immunity to background light and other spurious signal sources.